Oxidative bromination of imidazoheterocycle bromohydrates*

Abstract

bromides derivatives in oxidative bromination reactions has been studied. It has been established that reaction products structures and their yields depend on the properties of the substituents in the bicycle and the oxidant concentration.It is known [1,2] that the attack of electrophilic agents predominantly proceeds on the imidazole ring of imidazoheterocycles*. Among such reactions there is considerable interest in bromination because brominesubstituted imidazo[1,2-a]pyridines, imidazo[1,2-a]pyrimidines, and imidazo[2,1-b]thiazoles have found use as physiologically active substances [3] Most frequently bromination of the starting bases is carried out by bromine in chloroform [4], in acetic acid [5] or with the help of such brominating agents as N-bromosuccinimide and N-bromoacetamide in ethanol or carbon tetrachloride [6]. Interesting is the method of synthesis of bromo-substituted imidazoheterocycles by treating bromohydrates of the starting bases with an oxidizing agent. Note that carrying out this type of reaction in dimethyl sulfoxide, the solvent also acts as oxidant [7]. We have used hydrogen peroxide as oxidant in our work on the synthesis of bromo-substituted imidazo[1,2-a]pyridines [8,9] and also sodium nitrite in glacial AcOH (in particular in the synthesis of 5-bromo-6-(bromomethyl)imidazo[2,1-b]thiazole [10]).Earlier [8,11] we have synthesized bromides of imidazo[1,2-a]pyridinium, imidazo[1,2-a]pyrimidinium, and imidazo[2,1-b]thiazolium derivatives by interaction of the corresponding 2-aminoheterocycles with mono-or dihalo ketones. The reaction products were isolated as the salts 1a-g and converted into the dehydrated salts 2a-g. _______ *The term imidazoheterocycles means bicyclic heterosystems, one of the rings of which is imidazole (for example, imidazopyridine, imidazopyrimidine, and imidazothiazole).

10.1007/s11178-008-2012-9

“…The bromomethyl derivatives of imidazo[1,2-a]pyridine, imidazo [1,2-a]pyrimidine, and imidazo [2,1b]thiazole I, II [6,7] that we have previously synthesized can be by a known procedure converted into the corresponding cyanomethyl heterocycles III [8].…”